Photopolymerizable inkjet ink, ink cartridge, photopolymerizable composition, and coated matter

ABSTRACT

A photopolymerizable composition includes diethyleneglycol dimethacrylate, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one and 2-[2-hydroxy-4-(1-octyloxycarbonylethoxy)phenyl]-4,6-bis(4-phenyl)-4,6-bis)4-phenylphenyl-1,3,5-triazine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Applications Nos. 2013-097313 and 2014-035643, filed on May 7, 2013 and Feb. 26, 2014, respectively in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a photopolymerizable inkjet ink, an ink cartridge containing the ink, photopolymerizable composition and a coated matter.

2. Description of the Related Art

PCT Japanese published national phase application No. 2004-526820 discloses a photopolymerizable composition and a photopolymerizable inkjet ink using (meth)acrylic acid ester.

The present inventors have found some (meth)acrylic acid esters and (meth)acryl amides having no problem of skin sensitization. As disclosed in Japanese published unexamined application No. JP-2012-140593-A, they noticed that methacrylate is less toxic than acrylate and suggested an inkjet ink mainly using methacrylate.

Further, Japanese published unexamined applications Nos. JP-2013-181114-A and JP-2013-256659-A disclose a coating film having sufficient durability for the purpose of protecting surface. However, besides the sufficient durability, it is required that appearance is not changed even when exposed to direct sunlight.

When a solid coating film is formed without printing a specific design, spray coating or brush coating can be used instead of inkjet printing. However, it is difficult to form a coating film having high strength and good light resistance without a skin problem of skin sensitization.

The present inventors disclose in Japanese patent application No. 2012-215753 a coating film having low viscosity and high strength without a skin problem of skin sensitization.

Because of these reasons, a need exists for a photopolymerizable composition capable of forming a coating film having low viscosity, high strength and light resistance without a skin problem of skin sensitization.

SUMMARY

Accordingly, one object of the present invention is to provide a photopolymerizable composition capable of forming a coating film having low viscosity, high strength and light resistance without a skin problem of skin sensitization.

Another object of the present invention is to provide an inkjet ink using the photopolymerizable composition.

A further object of the present invention is to provide a cartridge containing the ink.

Another object of the present invention is to provide a coated matter using the photopolymerizable composition.

These objects and other objects of the present invention, either individually or collectively, have been satisfied by the discovery of a nonaqueous photopolymerizable composition, including diethyleneglycol dimethacrylate; 1-hydroxy-cyclohexyl-phenyl-ketone; 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one; and 2-[2-hydroxy-4-(1-octyloxycarbonylethoxy)phenyl]-4,6-bis(4-phenyl)-4,6-bis)4-phenylphenyl-1,3,5-triazine.

These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the detailed description when considered in connection with the accompanying drawings in which like reference characters designate like corresponding parts throughout and wherein:

FIG. 1 is a schematic view illustrating an example of an ink bag of the ink cartridge of the present invention; and

FIG. 2 is a schematic view illustrating an example of the ink cartridge of the present invention housing the ink bag.

DETAILED DESCRIPTION

The present invention provides a photopolymerizable composition capable of forming a coating film having low viscosity, high strength and light resistance without a skin problem of skin sensitization.

The photopolymerizable composition (ink) of the present invention includes at least diethyleneglycol dimethacrylate which is a methacrylic acid ester compound. A monomeric component including the methacrylic acid ester having a negative skin sensitization has high safeness, and preferably including acrylic acid ester has a viscosity capable of ejecting an inkjet as well. The 2-[2-hydroxy-4-(1-octyloxycarbonylethoxy)phenyl]-4,6-bis(4-phenyl)-4,6-bis)4-phenylphenyl-1,3,5-triazine improves light resistance and largely prevents yellowing. Since irradiation causes light curing and yellowing, when the photopolymerizable composition or its cured coating fully transmits light, curing is good, but yellowing is noticeable. When light is blocked, the cured coating cannot be formed. However, a combination of the 1-hydroxy-cyclohexyl-phenyl-ketone and the 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one as a polymerization initiator realizes non-conventional high curability and largely prevents yellowing.

A hindered amine compound further prevents yellowing while maintaining strength of the coating film.

The photopolymerizable composition negative for skin sensitization refers to a compound satisfying at least the following (1) or (2):

(1) a compound having a Stimulation Index (SI value) of less than 3, where the Stimulation Index indicates the level of sensitization as measured by a skin sensitization test based on the LLNA (Local Lymph Node Assay); and

(2) a compound evaluated as “negative for skin sensitization” or “no skin sensitization” in its MSDS (Material Safety Data Sheet).

Regarding the above (1), the compound having the SI value of less than 3 is considered as negative for skin sensitization as described in literatures, for example, “Functional Material” (Kino Zairyou) 2005, September, Vol. 25, No. 9, p. 55. The lower SI value means the lower level of skin sensitization. Thus, in the present invention, a monomer having the lower SI value is preferably used. The SI value of the monomer used is preferably less than 3, more preferably 2 or lower, and even more preferably 1.6 or lower.

Although easily-obtainable (meth)acrylic acid ester having a negative skin sensitization includes a material having poor polymerization reactivity, a photopolymerizable composition having sufficient curability and low viscosity is obtainable when used together with 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one.

The photopolymerizable composition preferably includes the polymerization initiator in an amount of from 10 to 20 parts by weight per 100 parts by weight of monomeric components because of having good light resistance and prevents itself from yellowing, but the amount is not limited thereto.

The photopolymerizable composition preferably includes the 2-[2-hydroxy-4-(1-octyloxycarbonylethoxy)phenyl]-4,6-bis(4-phenyl)-4,6-bis)4-phenylphenyl-1,3,5-triazine in an amount of from 0.5 to 0.9 parts by weight per 100 parts by weight of the (meth)acrylic acid ester because of having good light resistance and good photocurability, but the amount is not limited thereto.

The photopolymerizable composition of the present invention preferably includes caprolactone-modified dipentaerythritol hexaacrylate or ethyleneoxide-modified trimethylol propane trimethacrylate as a polymerizable monomer in addition to the diethyleneglycol dimethacrylate. The photopolymerizable composition preferably includes the caprolactone-modified dipentaerythritol hexaacrylate in an amount of from 3 to 15 parts by weight, and more preferably from 5 to 10 pasts by weight per 100 parts by weight of the (meth)acrylic acid ester monomer. The photopolymerizable composition preferably includes the ethyleneoxide-modified trimethylol propane trimethacrylate in an amount of from 15 to 60 parts by weight, and more preferably from 20 to 50 pasts by weight per 100 parts by weight of the (meth)acrylic acid ester monomer.

The photopolymerizable composition preferably includes the hindered amine compound in an amount of from 0.5 to 0.9 parts by weight per 100 parts by weight of the (meth)acrylic acid ester monomer, but the amount is not limited thereto. Plural hindered amines can be used together as triazine compounds can, e.g., a hindered amine having higher anti-degradation (self-oxidized quicker) and a hindered amine having less anti-degradation (slowly self-oxidized) can be used together.

The photopolymerizable composition preferably includes the diethyleneglycol dimethacrylate in an amount of from 10 to 95 parts by weight per 100 parts by weight of monomeric components.

The following (meth)acrylates and (meth)acryl amides can be used together as long as a resulting ink does not have a problem, even through they have a problem of skin sensitization in some degrees when used alone, or skin sensitization thereof is not confirmed.

Specific examples thereof include, but are not limited to, ethylene glycol di(meth)acrylate, hydroxypivalic acid neopentyl glycol di(meth)acrylate, α-butyrolactone acrylate, isobornyl(meth)acrylate, formalated trimethylol propane mono(meth)acrylate, polytetramethylene glycol di(meth)acrylate, trimethylol propane (meth)acrylic acid benzoate, diethyleneglycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂(9)], [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂ (n≈14)], [CH₂═CH—CO(OC₂H₄)_(n)—OCOCH═CH₂ (n≈23)], dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol dimethacrylate [CH₂═C(CH₃)—CO—(OC₃H₆)_(n)—OCOC(CH₃)═CH₂(n≈7)], 1,3-butanediol diacrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, propylene oxide-modified bisphenol A di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipentaerythritol hexa(meth)acrylate, (meth)acryloyl morpholine, 2-hydroxypropyl (meth)acryl amide, propylene oxide-modified tetramethylol methane tetra(meth)acrylate, dipentaerythritol hydroxypenta(meth)acrylate, caprolactone-modified dipentaerythritol hydroxypenta(meth)acrylate, ditrimethylol propane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, trimethylol propane acrylate, ethylene oxide-modified trimethylol propane triacrylate, propylene oxide-modified trimethylol propane tri(meth)acrylate, caprolactone-modified trimethylol propane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, propylene oxide-modified neopentyl glycol di(meth)acrylate, propylene oxide-modified glyceryl tri(meth)acrylate, polyester di(meth)acrylate, polyester tri(meth)acrylate, polyester tetra(meth)acrylate, polyester penta(meth)acrylate, polyester poly(meth)acrylate, N-vinyl caprolactam, N-vinyl pyrrolidone, N-vinyl formamide, polyurethane di(meth)acrylate, polyurethane tri(meth)acrylate, polyurethane tetra(meth)acrylate, polyurethane penta(meth)acrylate and polyurethane poly(meth)acrylate.

The diethyleneglycol dimethacrylate and (meth)acrylate or (meth)acrylamide usable therewith preferably have a weight ratio of from 100/0 to 3/97, and more preferably from 95/5 to 10/90, although depending on conditions such as curability and viscosity.

A photoradical polymerization initiator such as 1-hydroxy-cyclohexyl-phenyl-ketone and 2-hydroxy-2-methyl-1-phenylpropan-1-one is preferably used for the photopolymerizable composition of the present invention.

The (meth)acrylic acid ester and the (meth)acryl amide are known to have an ionic polymerizability as well. The ionic polymerization initiators are generally expensive and generate a slight amount of strong acid or strong alkali even in the state where they are not irradiated with light. Thus, it is necessary to take special cares such as imparting acid resistance and alkali resistance to an ink supply channel of an inkjet coating system, imposing limitation on the choice of members constituting the inkjet coating system.

In contrast, the ink of the present invention can use a photoradical polymerization initiator that is inexpensive and generates no strong acid or strong alkali. Thus, it is possible to produce an ink at low cost, and also it is easy to choose members of an inkjet coating system. When using a quite high energy light source, such as electron beams, α rays, β rays, γ rays or X rays, polymerization reaction can proceed without polymerization initiator. Since this is a conventionally known matter, the equipment is very expensive and the maintenance is complicated, this not described in detail in the present invention.

The photoradical polymerization initiators include, but are not limited to, a self-cleaving photopolymerization initiator and a hydrogen-abstracting polymerization initiator. These may be used alone, or in combination.

Specific examples of the self-cleaving photopolymerization initiator include, but are not limited to, 1-hydroxy-cyclohexyl-phenyl-ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)benzyl]phenyl}-2-methyl-1-propan-1-one, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)butan-1-one, bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, 2,4,6-trimethylbenzoylphosphine oxide, 1,2-octanedion[4-(phenylthio)-2-(o-benzoyloxime)], ethanone-1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime) and [4-(methylphenylthio)phenyl]phenylmethanone.

Specific examples of the hydrogen-abstracting polymerization initiator include, but are not limited to, benzophenone compounds such as benzophenone, methylbenzophenone, methyl-2-benzoylbenzoate, 4-benzoyl-4′-methyldiphenyl sulfide and phenylbenzophenone; and thioxanthone compounds such as 2,4-diethylthioxanthone, 2-chlorothioxanthone, isopropylthioxanthone and 1-chloro-4-propylthioxanthone.

Amines can be used together as a polymerization accelerator.

Specific examples thereof include, but are not limited to, p-dimethylaminobenzoate, 2-ethylhexyl p-dimethylaminobenzoate, methyl p-dimethylaminobenzoate, 2-dimethylaminoethyl benzoate and butoxyethyl p-dimethylaminobenzoate.

The photopolymerizable composition may be transparent without including a colorant, and may include a colorant when necessary. When the photopolymerizable composition is desired to be colorless or white, materials having less color are preferably used besides the polymerization initiator, the polymerization accelerator and the colorant.

Known inorganic pigments and organic pigments can be used as a colorant coloring the photopolymerizable composition.

Specific examples of black pigments include, but are not limited to, carbon black produced by a furnace method of a channel method.

Specific examples of yellow pigments include, but are not limited to, pigments of Pigment Yellow series, such as Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 75, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 114, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 129, Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 154, Pigment Yellow 155, and Pigment Yellow 180.

Specific examples of magenta pigments include, but are not limited to, pigments of Pigment Red series, such as Pigment Red 5, Pigment Red 7, Pigment Red 12, Pigment Red 48(Ca), Pigment Red 48(Mn), Pigment Red 57(Ca), Pigment Red 57:1, Pigment Red 112, Pigment Red 122, Pigment Red 123, Pigment Red 168, Pigment Red 184, Pigment Red 202, and Pigment Violet 19.

Specific examples of cyan pigments include, but are not limited to, pigments of Pigment Blue series, such as Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 15, Pigment Blue 15:3, Pigment Blue 15:4, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Vat Blue 4, and Vat Blue 60.

Specific examples of white pigments include, but are not limited to, sulfuric acid salts of alkaline earth metals such as barium sulfate; carbonic acid salts of alkaline earth metals such as calcium carbonate; silica such as fine silicic acid powder and synthetic silicic acid salts; calcium silicate; alumina; alumina hydrate; titanium oxide; zinc oxide; talc; and clay.

In addition, various inorganic or organic pigments may be optionally used considering, for example, physical properties of the photopolymerizable composition. Further, in the photopolymerizable composition, a polymerization inhibitor (e.g., 4-methoxy-1-naphthol, methylhydroquinone, hydroquinone, t-butylhydroquinone, di-t-butylhydroquinone, methoquinone, 2,2′-dihydroxy-3,3′-di(α-methylcyclohexyl)-5,5′-dimethyldiphenylmethane, p-benzoquinone, di-t-butyl diphenylamine, and 9,10-di-n-butoxyanthracene, 4,4′-[1,10-dioxo-1,10-decandiylbis(oxy)]bis[2,2,6,6-tetramethyl]-1-piperidinyloxy), a surfactant (e.g., higher fatty acid ester containing polyether, an amino group, a carboxyl group, or a hydroxyl group, a polydimethylsiloxane compound containing, in its side chain or terminal, polyether, an amino group, a carboxyl group, or a hydroxyl group, and a fluoroalkyl compound containing a polyether residue, an amino group, a carboxyl group, and a hydroxyl group), and a polar group-containing polymer pigment dispersing agent may be optionally used.

The ink of the present invention can be housed in a container, and used as an ink cartridge. With this form, users do not have to directly touch the ink during operations, such as exchange of the ink, and thus there is no concern about staining of their fingers, hands, clothes, etc. In addition, it is possible to prevent interfusion of foreign matter such as dust into the ink.

The container is not particularly limited, and a shape, structure, size, and material thereof can be appropriately selected depending on the intended purpose. As for the container, for example, preferred is a container having an ink bag formed of an aluminum laminate film, or a resin film.

The ink cartridge will be explained with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram illustrating one example of an ink bag 241 of the ink cartridge, and FIG. 2 is a schematic diagram illustrating the ink cartridge 200, in which the ink bag 241 of FIG. 1 is housed in a cartridge case 244.

As illustrated in FIG. 1, the ink bag 241 is filled with the ink by injecting the ink from an ink inlet 242. After removal of air present inside the ink bag 241, the ink inlet 242 is sealed by fusion bonding. At the time of use, a needle attached to the main body of the device is inserted into an ink outlet 243 formed of a rubber member to supply the ink to the device therethrough. The ink bag 241 is formed of a wrapping member such as an air non-permeable aluminum laminate film. As illustrated in FIG. 2, the ink bag 241 is typically housed in a plastic cartridge case 244, which is then detachably mounted in various inkjet recording devices to thereby use as the ink cartridge 200.

The ink cartridge of the present invention is preferably detachably mounted in inkjet recording devices. The ink cartridge can simplify the refill and exchange of the ink to improve workability.

As for a coating base for the ink of the present invention, paper, plastic, metal, ceramic, glass, or a composite material thereof is used. Since an absorbent base, such as wood free paper, can expect an effect of penetrating and drying, it is practical to use an aqueous ink or an oil ink, which is not a quick-drying ink, for such base. On the other hand, it is practical to use a quick-drying ink for a non-absorbent base, such as gloss coat paper, a plastic film, a plastic molded article, ceramic, glass, and metal.

The ink of the present invention is preferably used on, but is not limited to, the non-absorbent base of being immediately cured upon application of light. Among the non-absorbent bases, the ink of the present invention is suitably used for a plastic material, such as a plastic film, and a plastic molded article, which is formed of polyethylene, polypropylene, polyethylene terephthalate, polycarbonate, an ABS resin, polyvinyl chloride, polystyrene, any of other polyesters, polyamide, a vinyl-based material, or a composite material thereof.

EXAMPLES

Having generally described this invention, further understanding can be obtained by reference to certain specific examples which are provided herein for the purpose of illustration only and are not intended to be limiting. In the descriptions in the following examples, the numbers represent weight ratios in parts, unless otherwise specified.

<Evaluation Method of SI Value>

According to the skin sensitization test based on the LLNA (Local Lymph Node Assay), the SI value was measured in the manner described below.

[Test Material]

<<Positive Control>>

α-hexylcinnamaldehyde (HCA; product of Wako Pure Chemical Industries, Ltd.) was used as the positive control.

<<Medium>>

As a medium, a mixture containing acetone (product of Wako Pure Chemical Industries, Ltd.) and olive oil (product of Fudimi Pharmaceutical Co., Ltd.) in a volume ratio of 4/1 was used.

<<Animals Used>>

Before treated with the test substances, the positive control or the medium control, female mice were acclimated for 8 days including 6-day quarantine. No abnormalities were found in all the mice (used animals) during the quarantine/acclimation period.

Based on the body weights measured 2 days before the initiation of sensitization, they were categorized into 2 groups (4 mice/group) by the body weight stratified random sampling method so that the body weight of each individual was within ±20% of the average body weight of all the individuals. Each of the used animals was 8 weeks old to 9 weeks old at the time of the initiation of sensitization. The individuals remaining after the categorization were excluded from the test.

The used animals were individually identified by application of oil ink to their tale throughout the test period, and also their cages were labeled for identification.

<<Housing Environment>>

Throughout the housing period including the quarantine/acclimation period, the used animals were housed in an animal room with barrier system, which was set as follows: 21° C. to 25° C. in temperature, 40% to 70% in relative humidity, 10 times/hour to 15 times/hour in frequency of air circulation, and a 12 hour-interval lighting cycle (lighting from 7:00 to 19:00).

The housing cages used were those made of polycarbonate, and four animals were housed in each cage.

The used animals were given ad libitum solid feed for laboratory animals MF (product of Oriental Yeast Co., Ltd.). Also, using a water-supply bottle, the used animals were given ad libitum tap water in which sodium hypochlorite (PURELOX, product of OYALOX Co., Ltd.) had been added so that the chlorine concentration was about 5 ppm. Bedding used was SUNFLAKE (fir tree, shavings obtained with a power planer) (product of Charles River Inc.). The feed and all of the feeding equipments were sterilized with an autoclave (121° C., 30 min) before use.

The housing cage and the bedding were replaced with new ones at the times of the categorization and the removal of the auricular lymph node (i.e., the time when the animals were transferred from the animal room), and the water-supply bottle and rack were replaced with new ones at the time of the categorization.

[Test Method]

<<Group Composition>>

The group compositions of the medium control group and positive control group used for the measurement of the Si value are shown in Table 1.

TABLE 1 Sensitization Number of Sensitization dose Times of animals Test group substance (μL/auricle) sensitization (animal No.) Medium Medium 25 Once/day × 3 4 (1-4) control group only days Positive 25.0% HCA 25 Once/day × 3 4 (5-8) control group days [Preparation] <<Test Substance>>

Table 2 shows the amount of the test substance. The test substance was weighed in a measuring flask, and the volume of the test substance was adjusted to 1 mL with the medium. The thus-prepared test substance preparation was placed in a light-shielded airtight container (made of glass).

TABLE 2 Concentration after adjustment Mass of test (w/v %) substance (g) Test 50.0 0.5 substance <<Positive Control Substance>>

About 0.25 g of HCA was accurately weighed, and the medium was added to the HCA to have the volume of 1 mL, to thereby prepare a 25.0% by mass solution. The thus-prepared positive control substance preparation was placed in a light-shielded airtight container (made of glass).

<<BrdU>>

In a measuring flask, 200 mg of 5-bromo-2′-deoxyuridine (BrdU, product of NACALAI TESQUE, INC.) was accurately weighed in a measuring flask. Then, physiological saline (product of OTSUKA PHARMACEUTICAL CO., LTD.) was added to the measuring flask, and dissolved through application of ultrasonic waves. Thereafter, the volume of the resultant solution was adjusted to 20 mL to prepare a 10 mg/mL solution (BrdU preparation). The BrdU preparation was sterilized through filtration with a sterilized filtration filter and placed in a sterilized container.

<<Preparation Day and Storage Period>>

The positive control preparation was prepared on the day before the initiation of sensitization, and stored in a cold place except in use. The medium and the test substance preparations were prepared on the day of sensitization. The BrdU preparation was prepared 2 days before administration and stored in a cold place until the day of administration.

[Sensitization and Administration of BrdU]

<<Sensitization>>

Each (25 μL) of the test substance preparations, the positive control preparation or the medium was applied to both the auricles of each of the used animals using a micropipetter. This treatment was performed once a day for three consecutive days.

<<Administration of BrdU>>

About 48 hours after the final sensitization, the BrdU preparation (0.5 mL) was intraperitoneally administered once to each of the used animals.

[Observation and Examination]

<<General Conditions>>

All the used animals used for the test were observed once or more times a day from the day of the initiation of sensitization to the day of the removal of the auricular lymph node (i.e., the day when the animals were transferred from the animal room). Notably, the observation day was counted from the day of the initiation of sensitization being regarded as Day 1.

<<Measurement of Body Weights>>

The body weight of each of the used animals was measured on the day of the initiation of sensitization and on the day of the removal of the auricular lymph node (i.e., the day when the animals were transferred from the animal room). Also, the average of the body weights and the standard error thereof were calculated for each group.

<<Removal of Auricular Lymph Node and Measurement of Weight Thereof>>

About 24 hours after the administration of BrdU, the used animals were allowed to undergo euthanasia, and their auricular lymph nodes were sampled. The surrounding tissue of each auricular lymph node was removed, and the auricular lymph nodes from both the auricles were collectively weighed. Also, the average of the weights of the auricular lymph nodes and the standard error thereof were calculated for each group. After the measurement of the weights, the auricular lymph nodes of each individual were stored in a frozen state using a BIO MEDICAL FREEZER set to −20° C.

<<Measurement of BrdU Intake>>

After returning the auricular lymph nodes to room temperature, the auricular lymph nodes were mashed with the gradual addition of physiological saline, and suspended therein. The thus-obtained suspension was filtrated and then dispensed into the wells of a 96-well microplate, with 3 wells being used per individual. The thus-dispensed suspensions were measured for intake of BrdU by the ELISA method. The reagents used were those of a commercially available kit (Cell Proliferation ELISA, BrdU colorimetric, Cat. No. 1647229, product of Roche Diagnostics Inc.). A multiplate reader (FLUOSTAR OPTIMA, product of BMG LABTECH Inc.) was used to measure the absorbance of each well (OD: 370 nm to 492 nm, the intake of BrdU), and the average of the absorbance of the 3 wells for each individual was used as the measurement of BrdU for the individual.

[Evaluation of Results]

<<Calculation of Stimulation Index (SI)>>

As shown in the following formula, the measurement of BrdU intake for each individual was divided by the average of the measurements of BrdU intake in the vehicle control group to calculate the SI value for the individual. The SI value of each test group was the average of the SI values of the individuals. Also, the standard error of the SI values was calculated for each test group. Notably, the SI value was rounded at the second decimal place and shown to the first decimal place.

${SI} = \frac{\begin{matrix} {{{Average}\mspace{14mu}{of}\mspace{14mu}{measurements}\mspace{14mu}{of}\mspace{14mu}{BrdU}}\mspace{14mu}} \\ {{intake}\mspace{14mu}{for}\mspace{14mu}{each}\mspace{14mu}{individual}\mspace{14mu}\left( {{average}\mspace{14mu}{of}\mspace{14mu} 3\mspace{14mu}{wells}} \right)} \end{matrix}}{\mspace{14mu}\begin{matrix} {{Average}\mspace{14mu}{of}\mspace{14mu}{measurements}\mspace{14mu}{of}\mspace{14mu}{BrdU}\mspace{14mu}{intake}\mspace{14mu}{in}} \\ {{the}\mspace{14mu}{vehicle}\mspace{14mu}{control}\mspace{14mu}{group}\mspace{14mu}\left( {{average}\mspace{14mu}{of}\mspace{14mu} 4\mspace{14mu}{animals}} \right)} \end{matrix}}$

Example 1

The following materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 95 parts a2 5 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.5 parts

Details of a1 to a3, b1 and b2, c1, d1 and d2 are as follows. Values in ( ) at the ends are SI values in (1) LLNA test, and “None” means “negative for skin sensitization” or “no skin sensitization” in (2) MSDS (Material Safety Data Sheet).

a1: diethyleneglycol dimethacrylate “2G” from Shin-Nakamura Chemical Co., Ltd., (1.1)

a2: caprolactone-modified dipentaerythritol hexaacrylate DPCA 60 from Nippon Kayaku Co., Ltd. (Negative in MSDS)

a3: ethyleneoxide-modified trimethylolpropane trimethacrylate “TMPT-3EO” from Shin-Nakamura Chemical Co., Ltd., (1.0)

b1: 1-hydroxy cyclohexyl phenyl ketone “Irgacure 184” from BASF (Negative in MSDS)

b2: 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one “Irgacure 127” from BASF (Negative in MSDS)

c1: 2-[2-hydroxy-4-(1-octyloxycarbonylethoxy)phenyl]-4,6-bis(4-phenyl)-4,6-bis)4-phenylphenyl-1,3,5-triazine “TINUVIN479” from BASF (Negative in MSDS)

d1: sebacic acid bis[2,2,6,6-tetramethyl-1-(octyloxy)piperidine-4-yl] “TINUVIN123” from BASF (Negative in MSDS)

d2: a mixture of sebacic acid bis[1,2,2,6,6-pentamethyl-piperidine-4-yl] and sebacic acid [1,2,2,6,6-pentamethyl-piperidine-4-yl]methyl “TINUVIN292” from BASF (Positive in MSDS)

Example 2

The following materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 95 parts a2 5 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.5 parts (d) Hindered amine compound d1 0.5 parts

Example 3

The following materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 95 parts a2 5 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.9 parts (d) Hindered amine compound d1 0.9 parts

Example 4

The following materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 80 parts a2 20 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.5 parts

Example 5

The following materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 80 parts a2 20 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.5 parts (d) Hindered amine compound d1 0.5 parts

Example 6

The following materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 80 parts a2 20 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.9 parts (d) Hindered amine compound d1 0.9 parts

Example 7

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 8

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 9

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 10

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 11

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 12

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Example 13

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 14

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 15

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 16

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 17

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 18

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Example 19

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Table 6 to prepare an ink.

Example 20

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Table 6 to prepare an ink.

Example 21

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Table 6 to prepare an ink.

Example 22

The materials (a) to (d), and carbon black were mixed at ratios (parts by weight) shown in Table 6 to prepare an ink.

(a) (Meth)acrylic acid ester having negative skin sensitization a1 80 parts a2 20 parts (b) Photoradical polymerization initiator b1 15 parts b2 5 parts (c) Triazine compound c1 0.9 parts (d) Hindered amine compound d1 0.9 parts Carbon black 0.05 parts

Comparative Example 1

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 2

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 3

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 4

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 5

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 6

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 7

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 8

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 3-1 to 3-4 to prepare an ink.

Comparative Example 9

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 10

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 11

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 12

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 13

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 14

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 15

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 16

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 17

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 4-1 to 4-4 to prepare an ink.

Comparative Example 18

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 19

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 20

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 21

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 22

The materials (a) and (b) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 23

The materials (a) to (c) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 24

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

Comparative Example 25

The materials (a) to (d) were mixed at ratios (parts by weight) shown in Tables 5-1 to 5-4 to prepare an ink.

The viscosity (mPa·s) and the strength of coating film at 25, 45 and 60° C. of each ink were measured.

The viscosity of each ink was measured by a cone plate-type rotary viscometer (manufactured by TOKI SANGYO CO., LTD.) with the temperature of circulating water being constantly set 25, 45 and 60° C. The temperature of 25° C. is temperature set considering typical room temperature. The temperatures of 45 and 60° C. are temperatures of a heatable marketed inkjet ejection head such as GEN4 from Ricoh Printing Systems, Ltd.

The photopolymerizable composition prepared at a predetermined combination was used as it was in evaluation by brush coating. To evaluate inkjet ink, after the ink was filtered through a membrane filter made of fluorine resin, having a pore diameter of 5 microns, the ink was sealed in an aluminum pouch bag having the shape in FIG. 1 so that a bubble was formed. The pouch bag the ink was sealed in was contained in a plastic cartridge as shown in FIG. 2. In a chassis capable of containing the cartridge, an ink flow channel was formed from the cartridge to the GEN4 head from Ricoh Printing Systems, Ltd. to eject the ink and form a solid coating film. Each of the brush coating and the inkjet printing was controlled to form a solid coating film having a thickness about 40 microns.

A solid coating film formed on a marketed polycarbonate film (Iupilon E2000 having a thickness of 100 microns from Mitsubishi Engineering-Plastics Corp.) was irradiated at 0.3 W/cm² and 1,200 mJ/cm² and hardened so as to evaluate its strength and light resistance.

Scratch hardness of the irradiated and hardened coating film was evaluated by a pencil method specified in JIS-K-5600-5-4. Pencil hardness includes 2H, H, F, HB, B, 2B to 6B in descending order of hardness.

A coating film formed at 1,200 mJ/cm² was left sill under an insect collector fluorescent lamp FL15BL (15 W) from Toshiba Lighting & Technology Corp for 72 hrs, and the color tone of the coating film before and after exposed to the light was measured by 938 spectrodensitometer from X-rite, Inc. to evaluate yellowing as a color toner difference ΔE. The color tone was measured using 20 plain papers MY PAPER from Ricoh Company, Ltd., having a weight of 64 g/m².

When the photopolymerizable composition is used as an inkjet ink, the ink preferably has properties meeting with required specifications of an inkjet ejection head used. Various ejection heads are marketed from many manufacturers, and some of them have large ejection power to eject an ink having high viscosity and wide thermostat. The ink preferably has a viscosity of from 2 to 150 mPa·s, and more preferably from 5 to 18 mPa·s at 25° C. However, the thermostat of the ejection head can be used. When the viscosity is too high at 25° C., the head may be heated when necessary to make the ink have lower viscosity. When heated at from 45 to 60° C., the ink preferably has a viscosity of from 5 to 18 mPa·s thereat.

TABLE 3-1 Comparative Comparative Comparative Comparative Material Example 1 Example 2 Example 3 Example 4 a a1 95 95 95 95 a2  5  5  5  5 a3 b b1 20 20 20 20 b2 c c1   0.5   0.5   0.9 d d1 05   0.9 d2 Carbon Black*1 25° C. Viscosity  8  8  9 10 45° C. Viscosity *2 *2 *2 *2 60° C. Viscosity *2 *2 *2 *2 Inkjet Ejection head 25° C. 25° C. 25° C. 25° C. Printing temperature Coating film strength F F F Less than 6B (1200 mj/cm²) ΔE 12  8  7  2 Brush Coating film strength F F F Less than 6B Coating (1200 mj/cm²) ΔE 12  8  7  2

TABLE 3-2 Material Example 1 Example 2 Example 3 a a1 95 95 95 a2  5  5  5 a3 b b1 15 15 15 b2  5  5  5 c c1   0.5   0.5   0.9 d d1   0.5   0.9 d2 Carbon Black*1 25° C. Viscosity  9  9 10 45° C. Viscosity *2 *2 *2 60° C. Viscosity *2 *2 *2 Inkjet Ejection head 25° C. 25° C. 25° C. Printing temperature Coating film 2H 2H H strength (1200 mj/cm²) ΔE  8  7  2 Brush Coating film 2H 2H H Coating strength (1200 mj/cm²) ΔE  8  7  2

TABLE 3-3 Comparative Comparative Comparative Comparative Material Example 5 Example 6 Example 7 Example 8 a a1 80 80 80 80 a2 20 20 20 20 a3 b b1 20 20 20 20 b2 c c1   0.5   0.5   0.9 d d1 05   0.9 d2 Carbon Black*1 25° C. Viscosity 16 17 17 18 45° C. Viscosity  8  8  9  9 60° C. Viscosity *2 *2 *2 *2 Inkjet Ejection head 45° C. 45° C. 45° C. 45° C. Printing temperature Coating film strength F F F Less than 6B (1200 mj/cm²) ΔE 13  8  7  2 Brush Coating film strength F F F Less than 6B Coating (1200 mj/cm²) ΔE 13  8  7  2

TABLE 3-4 Material Example 4 Example 5 Example 6 a a1 80 80 80 a2 20 20 20 a3 b b1 15 15 15 b2  5  5  5 c c1   0.5   0.5   0.9 d d1   0.5   0.9 d2 Carbon Black*1 25° C. Viscosity 18 18 19 45° C. Viscosity  8  9 10 60° C. Viscosity *2 *2 *2 Inkjet Ejection head 45° C. 45° C. 45° C. Printing temperature Coating film 2H 2H H strength (1200 mj/cm²) ΔE  8  7  2 Brush Coating film 2H 2H H Coating strength (1200 mj/cm²) ΔE  8  7  2

TABLE 4-1 Comparative Comparative Comparative Comparative Material Example 9 Example 10 Example 11 Example 12 a a1 50 50 50 50 a2 50 50 50 50 a3 b b1 10 10 10 10 b2 c c1 0.5 0.5 0.9 d d1 05 0.9 d2 Carbon Black*1 25° C. Viscosity 55 56 57 59 45° C. Viscosity 22 22 23 24 60° C. Viscosity 13 13 14 14 Inkjet Ejection head 60° C. 60° C. 60° C. 60° C. Printing temperature Coating film strength F F F Less than 6B (1200 mj/cm²) ΔE 7 4 3 2 Brush Coating film strength F F F Less than 6B Coating (1200 mj/cm²) ΔE 7 4 3 2

TABLE 4-2 Material Example 7 Example 8 Example 9 a a1 50 50 50 a2 50 50 50 a3 b b1 7.5 7.5 7.5 b2 2.5 2.5 2.5 c c1 0.5 0.5 0.9 d d1 0.5 0.9 d2 Carbon Black*1 25° C. Viscosity 57 58 60 45° C. Viscosity 22 24 25 60° C. Viscosity 13 14 14 Inkjet Ejection head 60° C. 60° C. 60° C. Printing temperature Coating film 2H 2H H strength (1200 mj/cm²) ΔE 4 3 2 Brush Coating film 2H 2H H Coating strength (1200 mj/cm²) ΔE 4 3 2

TABLE 4-3 Comparative Comparative Comparative Comparative Material Example 13 Example 14 Example 15 Example 16 a a1 50 70 70 70 a2 50 10 10 10 a3 20 20 20 b b1 15 15 15 b2 10 c c1   0.9   0.5   0.5 d d1   0.9 05   0.9 d2 Carbon Black*1 25° C. Viscosity *3 14 15 15 45° C. Viscosity *3  7  7  7 60° C. Viscosity *3 *2 *2 *2 Inkjet Ejection head *3 45° C. 45° C. 45° C. Printing temperature Coating film strength *3 H H H (1200 mj/cm²) ΔE *3  9  6  5 Brush Coating film strength *3 H H Less than 6B Coating (1200 mj/cm²) ΔE *3  9  6  5

TABLE 4-4 Comparative Material Example 17 Example 10 Example 11 Example 12 a a1 70 70 70 70 a2 10 10 10 10 a3 20 20 20 20 b b1 15 11 11 11 b2  4  4  4 c c1   0.9   0.5   0.5   0.9 d d1   0.9 05   0.9 d2 Carbon Black*1 25° C. Viscosity 45° C. Viscosity 60° C. Viscosity *2 *2 *2 *2 Inkjet Ejection head 45° C. 45° C. 45° C. 45° C. Printing temperature Coating film strength Less than 6B 2H 2H H (1200 mj/cm²) ΔE  2  6  5  2 Brush Coating film strength Less than 6B 2H 2H H Coating (1200 mj/cm²) ΔE  2  6  5  2

TABLE 5-1 Comparative Comparative Comparative Comparative Material Example 18 Example 19 Example 20 Example 21 a a1 10 10 10 10 a2 a3 90 90 90 90 b b1 20 20 20 20 b2 c c1 0.5 0.5 0.9 d d1 05 0.9 d2 Carbon Black*1 25° C. Viscosity 18 19 20 21 45° C. Viscosity 15 15 16 17 60° C. Viscosity 9 9 10 10 Inkjet Ejection head 60° C. 60° C. 60° C. 60° C. Printing temperature Coating film strength H H H Less than 6B (1200 mj/cm²) ΔE 14 8 7 2 Brush Coating film strength H H H Less than 6B Coating (1200 mj/cm²) ΔE 14 8 7 2

TABLE 5-2 Material Example 13 Example 14 Example 15 a a1 10 10 10 a2 a3 90 90 90 b b1 15 15 15 b2 5 5 5 c c1 0.5 0.5 0.9 d d1 0.5 0.9 d2 Carbon Black*1 25° C. Viscosity 20 21 21 45° C. Viscosity 15 16 18 60° C. Viscosity 9 10 10 Inkjet Ejection head 60° C. 60° C. 60° C. Printing temperature Coating film 2H 2H H strength (1200 mj/cm²) ΔE 8 7 2 Brush Coating film 2H 2H H Coating strength (1200 mj/cm²) ΔE 8 7 2

TABLE 5-3 Comparative Comparative Comparative Comparative Material Example 22 Example 23 Example 24 Example 25 a a1 50 50 50 50 a2 a3 50 50 50 50 b b1 20 20 20 20 b2 c c1   0.5   0.5   0.9 d d1 05   0.9 d2 Carbon Black*1 25° C. Viscosity 16 17 17 18 45° C. Viscosity  8  8  9  9 60° C. Viscosity *2 *2 *2 *2 Inkjet Ejection head 45° C. 45° C. 45° C. 45° C. Printing temperature Coating film strength H H H Less than 6B (1200 mj/cm²) ΔE 13  8  7  2 Brush Coating film strength H H H Less than 6B Coating (1200 mj/cm²) ΔE 13  8  7  2

TABLE 5-4 Material Example 16 Example 17 Example 18 a a1 50 50 50 a2 a3 50 50 50 b b1 15 15 15 b2  5  5  5 c c1   0.5   0.5   0.9 d d1   0.5   0.9 d2 Carbon Black*1 25° C. Viscosity 17 18 18 45° C. Viscosity  8  9  9 60° C. Viscosity *2 *2 *2 Inkjet Ejection head 45° C. 45° C. 45° C. Printing temperature Coating film 2H 2H H strength (1200 mj/cm²) ΔE  8  7  2 Brush Coating film 2H 2H H Coating strength (1200 mj/cm²) ΔE  8  7  2

TABLE 6 Material Example 19 Example 20 Example 21 Example 22 a a1 50 50 50 50 a2 50 50 50 50 a3 b b1 7.5 7.5 7.5 7.5 b2 2.5 2.5 2.5 2.5 c c1 0.9 0.8 0.9 0.9 d d1 0.7 0.9 0.9 d2 0.9 Carbon Black*1 0.05 25° C. Viscosity 60 60 60 62 45° C. Viscosity 25 25 25 26 60° C. Viscosity 14 14 14 15 Inkjet Ejection head 60° C. 60° C. 60° C. 60° C. Printing temperature Coating film strength 2H 2H 2H H (1200 mj/cm²) ΔE 2 2 2 2 Brush Coating film strength 2H 2H 2H H Coating (1200 mj/cm²) ΔE 2 2 2 2 *1: Carbon black #10 from Mitsubishi Chemical Corp. and a dispersing agent “Solsperse39000” manufactured by Lubrizol Japan Co., with the weight ratio of 3/1. *2: Viscosity was not measured because the ink was ejectable at lower temperature. *3: Not uniformly dissolved, and not evaluated.

A comparison between Comparative Examples 2 to 4 and Examples 1 to 3, Comparative Examples 6 to 8 and Examples 4 to 6, Comparative Examples 10 to 12 and Examples 13 to 15 or Comparative Examples 23 to 25 and Examples 16 to 18 proves that a combination of 1-hydroxy-cyclohexyl-phenyl-ketone and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one improves strength of the coating film. Particularly, a comparison between Comparative Example 4 and Example 3, Comparative Example 8 and Example 6, Comparative Example 12 and Example 9, Comparative Example 17 and Example 12, Comparative Example 21 and Example 15 or Comparative Example 25 and Example 18 proves that only the 1-hydroxy-cyclohexyl-phenyl-ketone is difficult to obtain practical curability to achieve low yellowing ΔE=2 which is hard to visually observe, but the combination of 1-hydroxy-cyclohexyl-phenyl-ketone and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one achieves high light resistance and practically sufficient strength of the coating film.

In addition, a hindered amine compound is proved to further decrease ΔE and improve light resistance when used together. Examples 19 to 21 prove high light resistance and practically sufficient strength of the coating film can be achieved even when the content ratio of the triazine compound and the hindered amine compounds is changed or the hindered amine is changed. However, even a component included in a small amount preferably has negative skin sensitization, and a material having a problem of skin sensitization such as a mixture of sebacic acid bis[1,2,2,6,6-pentamethyl-piperidine-4-yl] and sebacic acid [1,2,2,6,6-pentamethyl-piperidine-4-yl]methyl is preferably included in a minimum amount.

Example 22 proves high light resistance and practically sufficient strength of the coating film can be achieved even when a colorant is included to color the composition to a light color.

Ethyleneoxide-modified trimethylol propane trimethacrylate has a formula [CH₃CH₂C—{CH₂(O—CH₂CH₂)_(x)—OCOC(CH₃)—CH₂}₃]. X represents a length of ethyleneoxide part. The larger the X, the larger the molecular weight and the higher the viscosity. The higher the viscosity, the more difficult to use as an inkjet ink material. However, monomers of a4 to a8 are expected to improve processing suitability. It is preferable not to use trimethylol propane trimethacrylate (x=0) because of having a symbol mark “N” representing environmental dangerous hazardousness and a risk phrase “R51/53” representing acute aquatic toxicity and long-term adverse affect in EU. Directive 67/548/EEC in consideration of influence on the environment. X of the ethyleneoxide-modified trimethylol propane trimethacrylate used in Examples is 1. The ethyleneoxide-modified trimethylol propane trimethacrylate does not have a problem of viscosity as a material included in an inkjet ink. The photopolymerizable composition including this forms a coating film having sufficient strength. Further, the ethyleneoxide-modified trimethylol propane trimethacrylate has no problem of skin sensitization, environmental dangerous hazardousness, acute aquatic toxicity and long-term adverse affect. X may be larger when necessary.

There were no noticeable differences between coating films formed by the inkjet printing and the brush coating. All the photopolymerizable compositions and the inks had no particular odors to be cautioned.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of the invention as set forth therein. 

What is claimed is:
 1. An inkjet ink, comprising a photopolymerizable composition, comprising: (a) a monomeric component comprising (a1) diethyleneglycol dimethacrylate (b1) 1-hydroxy-cyclohexyl-phenyl-ketone; (b2) 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)benzyl]phenyl}-2-methyl-1-propane-1-one; and (c) 2-[2-hydroxy-4-(1-octyloxycarbonylethoxyl)phenyl]-4,6-bis(4-phenylphenyl)-1,3,5-triazine, wherein the inkjet ink has a viscosity of from 2 to 150 mP·s at 25° C., and is adapted for ejection through an inkjet ejection head.
 2. The inkjet ink of claim 1, wherein the photopolymerizable composition further comprises (a2) caprolactone-modified dipentaerythritol hexaacrylate.
 3. The inkjet ink of claim 1, wherein the photopolymerizable composition further comprises (a3) ethyleneoxide-modified trimethylolpropane trimethacrylate.
 4. The inkjet ink of claim 1, wherein the photopolymerizable composition further comprises a hindered amine compound.
 5. The inkjet ink of claim 4, wherein the hindered amine compound is (d1) sebacic acid bis[2,2,6,6-tetramethyl-1-(octyloxy)piperidine-4-yl].
 6. A cartridge containing the ink according to claim
 1. 7. The inkjet ink of claim 1, wherein the composition has a Stimulation Index (SI value) of less than
 3. 8. The inkjet ink of claim 1, wherein the composition is negative for skin sensitization.
 9. The inkjet ink of claim 7, wherein the composition is negative for skin sensitization.
 10. The inkjet ink of claim 1, wherein components (b1) and (b2) are present in a total amount of from 10 to 20 parts by weight per 100 parts by weight of monomeric components of the composition.
 11. The inkjet ink of claim 1, wherein component (c) is present in an amount of from 0.5 to 0.9 parts by weight per 100 parts by weight of monomeric components of the composition.
 12. The inkjet ink of claim 2, wherein component (a2) is present in an amount of from 3 to 15 parts by weight per 100 parts by weight of monomeric components of the composition.
 13. The inkjet ink of claim 3, wherein component (a3) is present in an amount of from 50 to 60 parts by weight per 100 parts by weight of monomeric components of the composition.
 14. The inlet ink of claim 4, wherein the hindered amine compound is present in an amount of from 0.5 to 0.9 parts by weight per 100 parts by weight of monomeric components of the composition.
 15. The inkjet ink of claim 1, wherein component (a1) is present in an amount of from 10 to 95 parts by weight per 100 parts by weight of monomeric components of the composition.
 16. The inkjet ink of claim 1, wherein component (a1) is present in an amount of from 50 to 95 parts by weight per 100 parts by weight of monomeric components of the composition.
 17. The inkjet ink of claim 1, wherein the viscosity is from 5 to 18 mPa·s at 25° C.
 18. The inkjet ink of claim 1, wherein the viscosity is from 5 to 18 mPa·s at 60° C. 